Journal of the Korean Physical Society, Vol. 45, No. 5, November 2004, pp. 1158∼1161

All-Optical Logic Gates Using SemiconductorOptical-Amplifier-Based Devices and Their Applications

Jae Hun Kim, Young Il Kim, Young Tae Byun,∗ Young Min Jhon, Seok Lee, Sun Ho Kim and Deok Ha Woo

Photonics Research Center, Korea Institute of Science and Technology, Seoul 136-791

(Received 7 July 2004)

By using two main effects of cross-gain modulation and cross-phase modulation in semiconductoroptical amplifier-based devices, many logic functions of logic AND, OR, XOR, NOR and XNORare successfully demonstrated. Also, complex systems including all-optical half and full adders in acombination of multiple logic functions are successfully demonstrated. These functions will providenot only increased speed and capacity of telecommunication systems, but also various functionalitiesincluding optical packet switching, decision making, basic or complex optical computing, and manyother optical signal-processing systems.

PACS numbers: 42.79.T, 42.65.P, 85.30Keywords: Optical logic gate, Semiconductor optical amplifier, Cross-gain modulation

I. INTRODUCTION

As the speed of telecommunication systems increasesand reaches the limit of electronic devices, the de-mand for all-optical logic operations such as switch-ing, decision-making, regenerating, and basic or complexcomputing is rapidly increasing. All-optical logic gatesare essential elements for optical signal processors andnetworks.

Many researchers have reported their own logic gates,including NOR using a semiconductor optical amplifier(SOA) [1], OR with NOR using an ultrafast nonlinearinterferometer (UNI) [2], XOR using a terahertz opticalasymmetric demultiplexer (TOAD) [3], and so on. Eventhough logic gates using the UNI and the TOAD havethe advantage of high speed, they are very complex anddifficult to integrate with other logic gates. Contraryto these devices, SOA-based devices are compact, sta-ble, integration-capable, and potentially independent ofpolarization and wavelength [4]. Also, they have the ad-vantages of low switching energy and low latency [5]. Inthis paper, SOA-based devices are mainly employed toembody the fundamental logic functions.

II. VARIOUS ALL-OPTICAL LOGIC GATESUSING XPM AND XGM

∗E-mail: byt427@kist.re.kr;Tel: +82-2-958-5797; Fax: +82-2-958-5709

1. All-Optical AND Gate Using XPM

To accomplish an all-optical AND logic gate [6], anXPM wavelength converter (Alcatel 1901 ICM) has beenutilized. The experimental setup is shown in Figure 1.Signals A and B with patterns 1100 and 0110 are coupledinto the XPM wavelength converter to procure the AND

Fig. 1. Experimental setup for logic AND.

Fig. 2. Experimental results of logic AND.

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All-Optical Logic Gates Using Semiconductor· · · – Jae Hun Kim et al. -1159-

gate signal.The input and output signals are configured in Fig-

ure 2. Overlapping signal A with signal B produces anoutput signal with the pattern 0100, which is the correctproof for characteristics of an AND logic gate. Therefore,the all-optical AND gate has been successfully demon-strated at 20 Gb/s. The all-optical XNOR gate has beenrealized by using the static characteristics of the XPMwavelength converter [7].

2. All-Optical NOR Gate Using XGM

By using cross-gain modulation (XGM), an all-opticalNOR gate has been demonstrated at 10 Gb/s [8]. Theconfiguration of the experimental setup is shown in Fig-ure 3. Signals A and B with patterns 1100 and 0110 areadded to form the signal A + B, which has the signalset of (1,0), (1,1), (0,1), and (0,0). A clock signal withrepetition rate of 10 GHz is used as probe signal. Clocksignal and signal A + B are simultaneously injected intothe SOA. Due to the gain saturation effect of the SOA,the output signal has logic state 1 when only (0,0) ofinput appears. Input and output signals are seen in Fig-ure 4. As shown in Figure 4, output is logic 1 whenboth inputs A and B are logic 0. Otherwise, output islogic 1. Since these results coincide with logic NOR,the all-optical NOR gate has been successfully demon-strated at 10 Gb/s. The all-optical OR gate can also be

Fig. 3. Experimental setup for logic NOR.

Fig. 4. Experimental results for logic NOR.

obtained with one additional SOA incorporated with theall-optical NOR gate [9].

3. All-Optical XOR Gate Using XGM

By using two SOAs, an all-optical XOR gate has beendemonstrated at 10 Gb/s [10]. Figure 5 shows the exper-imental setup for realizing the all-optical XOR gate. Bypassing signal A with the pattern 1100 as probe signaland signal B with the pattern 0110 as pump signal intoSOA-1, Boolean AB with the pattern 1000 has been ob-tained. Also, by switching the roles of signal A and B forSOA-2, Boolean AB with the pattern 0010 has been ac-quired. After combining Boolean AB and AB with the50:50 coupler, the output signal has been detected anddisplayed on the signal analyzer. Figure 6 depicts theadded signal of Boolean AB and AB, which is BooleanAB + AB with the pattern 1010. As shown in Figure 6,the output signal is logic 1 when either signal A or B islogic 1. When both signals A and B have the same logicstate, the output signal is logic 0. These results coincidewith logic XOR. Therefore, the all-optical XOR gate at10 Gb/s has been successfully realized.

4. All-Optical AND Gate using XGM

Fig. 5. Experimental setup for logic XOR.

Fig. 6. Experimental results for logic XOR.

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To compose the all-optical AND gate, two SOAs arerequired [11]. The experimental setup is shown in Figure7. Firstly, by passing signal A as probe signal and signalB as pump signal into SOA-2, Boolean AB can be ob-tained [2]. Then, clock signal as probe signal and signalB as pump signal are simultaneously injected throughSOA-1 to produce the gain inversion of signal B, whichis Boolean B. Boolean B out of AB is substituted bythe output of SOA-1 to obtain Boolean AB, which co-incides with logic AND. Figure 8 shows the input andoutput signals.

III. COMPLEX LOGIC SYSTEMS:ALL-OPTICAL HALF ADDER AND

FULL ADDER

By using the SOA-based devices, an all-optical halfadder as a simple example of further complex systemshas been demonstrated [12]. To realize logic SUM andCARRY of the half adder, the all-optical XOR and ANDgates are utilized, respectively. Figure 9 shows the ex-perimental setup for realizing the all-optical half adder.Figure 10 depicts logic SUM and CARRY of the halfadder. Both logic SUM and CARRY are simultaneouslyperformed to prove the half-adder operation at 10 Gb/s.

Fig. 7. Experimental setup for the all-optical AND gate.

Fig. 8. Input and output signals of the all-optical ANDgate.

Fig. 9. Experimental setup for the all-optical half adder.

Fig. 10. Experimental results of half adder.

Fig. 11. Experimental setup for all-optical full adder in-cluding SUM and CARRY.

The all-optical full adder requires much higher com-plexity than the all-optical half adder [13]. A total of 8SOAs are required. To realize SUM and CARRY, twoXOR gates and four NOR gates are utilized. The ex-perimental setup to implement the all-optical XOR andNOR gates for SUM and CARRY is shown in Figure11. By injecting signals A and B through the first XORgate, Boolean AB + AB is obtained. By injecting sig-nals AB + AB and C through the second XOR gate,signal SUM of full adder is obtained.

By injecting signals A + B and clock through SOA-

All-Optical Logic Gates Using Semiconductor· · · – Jae Hun Kim et al. -1161-

Fig. 12. Experimental results of the all-optical full adder.

5, all-optical NOR operation of A + B, Boolean ¯A+Bis obtained. With the same methods but with variationof input signals, NOR operation of B + C and C + Ais also obtained. The added signal of these outputs isinjected with the clock signal through SOA-8 to obtainthe signal CARRY of the all-optical full adder. The inputand output signals are shown in Figure 12.

IV. CONCLUSION

In this paper, the fundamental all-optical logic gatesincluding AND, OR, NOR, XNOR, and XOR by usingthe SOA-based devices are demonstrated. Also, the all-optical half adder and full adder as examples of furthercomplex systems are demonstrated. The operation speedof the all-optical logic gates is limited to around 10 Gbps,except for the AND gate using XPM. This low speed isdue to the carrier recovery time in SOA. To overcomethis problem, two cascaded SOAs and a much longerSOA are good alternatives [14,15]. Realization of the all-optical logic gates will provide not only increased speedand capacity of telecommunication systems, but also var-ious functionalities including optical packet switching,add/drop, decision making, bit exactraction, regenerat-ing, and basic or complex optical computing.

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